Why is a default method needed in an interface?

A default method in an interface is used to provide an implementation of a method directly within the interface, without forcing all classes that implement it to override this method.

This allows:

• Adding new methods to an interface without breaking existing implementations.
• Providing a default behavior that can be overridden if necessary.

For example, in Java 8, default methods enable extending interfaces without breaking backward compatibility.

Example in Java:

public interface Logger {
    void log(String message);

    default void logError(String error) {
        log("ERROR: " + error);
    }
}

Here, logError has a default implementation, and classes implementing Logger may not need to write this method if the default behavior suits them.